Transparent lenses are used to provide structure and protection to displays, such as on mobile phones. Typical lenses include glass lenses and plastic lenses.
Glass lenses, such as Gorilla Glass, available from Corning Incorporated, Dragontail, available from Asahi Glass Co., Ltd., and Xensation, available from SCHOTT North America, Inc., are formed from alumino-silicate glass that is hardened or strengthened by using a potassium or lithium ion bath. These lenses typically exhibit good scratch resistance, but suffer from poor fracture resistance. In addition, glass lenses may have a limited amount of three-dimensional effect imparted to the glass surface by grinding or polishing the lens, but the extent of the effect is limited.
Plastic lens, such as those using polycarbonate (PC) and poly(methyl methacrylate) (PMMA), allow for the lens to be shaped to provide a three dimensional effect, but typically suffer from poor abrasion resistance. To improve abrasion resistance, a hard coating may be applied to the surface of the plastic lens. Exemplary coatings may be purely siloxane, purely organic such as acrylic or epoxy, or they may include a siloxane/organic interpenetrating network (IPN). The hard coating is typically about 8 microns to about 10 microns in thickness, and are available in a range of harnesses. While the typical hard coatings improve the scratch resistance of the plastic lens, the overall scratch resistance is still inferior that that of a glass lens.
More advanced coatings, such as diamond like carbon (DLC) and diamond like nano-composites (DLN) are also available. However, such coatings are typically applied directly to the glass or plastic substrate, or to a thin adhesion promoting layer. When applied in such a matter to a plastic substrate, these very hard coatings will fail prematurely.